Brenneman earned his B.A. in Secondary Education/Spanish from Lock Haven University, and returned to his hometown to teach Spanish at his former high school for three years, which is where his nickname 'the Spaniard' came from.[4] He continued his education, earning his Masters from East Stroudsburg University of Pennsylvania in Sports Management. It was during the first season of the Pros vs Joes game show when he first received national public attention. He was unexpectedly cast after submitting his application to participate in the reality game show, but he won the competition alongside his older brother Ben.[5] Following his victory on the Pros vs. Joes show, Brenneman resigned from his high school teaching job to pursue a mixed martial arts fighting career.

During his amateur career, Brenneman compiled a 5–0 undefeated record. In an attempt to maintain his momentum, he quickly turned professional, debuting on July 28, 2007, against Marcello Olivera. Brenneman also earned a 5–0 record at the professional level through early 2008, with a notable split-decision victory over Drew Puzon at the ShoXC event on January 25, 2008.[6][7]

During a sparring session with one-time UFC fighter Chris Liguori, Brenneman sustained a kick to the face that shattered his left orbital and forced him to undergo emergency surgery to repair the damage. Vertical and lateral plates were inserted into his face, and he eventually regained vision in his left eye. Brenneman made his comeback to competition on September 12, 2008, against John Howard, but suffered the first loss of his career. Because of the defeat, the self-trained Brenneman decided to join the AMA Fight Club,[5] and went on to win his next six bouts before being offered a contract for the Ultimate Fighting Championship (UFC).

Brenneman faced Amilcar Alves on January 22, 2011, at UFC Fight Night 23.[8] He won the fight via unanimous decision.

Brenneman was scheduled to fight TJ Grant on June 26, 2011 at UFC on Versus 4, but Grant had to pull out due to illness and the fight was scrapped.[9] However, just hours before the weigh-ins it was reported that Nate Marquardt did not receive medical clearance and had to pull out of his bout against Rick Story. As a result, Brenneman fought Story in the evening's co-main event. Brenneman upset the favored Story, as Brenneman was able to out wrestle Story and control him on the ground while fending off multiple submission attempts in the third round en route to a unanimous decision victory. He later stated about his upset win, that he'd luckily been told about being Marquardt's replacement for this fight earlier than Story and was also training for a fight with Story as well because of this, just in case he turned out to be the replacement, which he was.[10]

Brenneman was expected to face Kyle Noke on September 1, 2012 at UFC 151.[14] However, as a result of the cancellation of UFC 151, Noke/Brenneman was rescheduled for September 22, 2012 at UFC 152.[15] Brenneman lost the fight in the first round via TKO due to punches. After the loss Brenneman was released from the promotion.[16]

Brenneman cut down to 155 lbs. following his release from the UFC.[17] Brenneman fought Eric Irvin at VFL 40 on Jan 19, 2013. He won via second round submission. Brenneman defeated Jeremy Castro and Gemiyale Adkins in the Cage Fury Fighting Championships, and would then defeat Kyle Baker by submission via arm-triangle choke for the vacant CFFC lightweight title.[18]

Brenneman returned to the UFC and faced promotional newcomer Beneil Dariush in a lightweight bout on January 15, 2014 at UFC Fight Night 35, replacing an injured Jason High.[19] Brenneman was quickly submitted in the first round via rear-naked choke, after being dropped by a left hand.

Brenneman faced Leandro Silva on November 8, 2014 at UFC Fight Night 56.[22] Brenneman was submitted by a rear naked choke in the first round following multiple takedown attempts. After the loss Brenneman was again released from the promotion.[23]